P—N—P ligand

ABSTRACT

A new P-N-P ligand is useful in ethylene oligomerizations. In combination with i) a source of chromium; and ii) an activator such as methylalumoxane; the ligand of this invention may be used to prepare an oligomer product that contains a mixture of high purity alpha olefins. In a preferred embodiment, the ligand of this invention enables a selective oligomerization in which the majority of the liquid product is a mixture of hexene and octene. The amount of by-product polymer that is produced in preferred oligomerization reactions is advantageously low.

TECHNICAL FIELD

This invention provides a new family of P-N-P ligands. The ligands areuseful in ethylene oligomerization reactions. The ligands arecharacterized by having at least one aromatic fluorocarbyl alkoxidegroup bonded to a P atom.

BACKGROUND ART

Alpha olefins are commercially produced by the oligomerization ofethylene in the presence of a simple alkyl aluminum catalyst (in the socalled “chain growth” process) or alternatively, in the presence of anorganometallic nickel catalyst (in the so called Shell Higher Olefins,or “SHOP” process). Both of these processes typically produce a crudeoligomer product having a broad distribution of alpha olefins with aneven number of carbon atoms (i.e. butene-1, hexene-1, octene-1 etc.).The various alpha olefins in the crude oligomer product are thentypically separated in a series of distillation columns. Butene-1 isgenerally the least valuable of these olefins as it is also produced inlarge quantities as a by-product in various cracking and refiningprocesses. Hexene-1 and octene-1 often command comparatively high pricesbecause these olefins are in high demand as comonomers for linear lowdensity polyethylene (LLDPE).

Technology for the selective trimerization of ethylene to hexene-1 hasbeen recently put into commercial use in response to the demand forhexene-1. The patent literature discloses catalysts which comprise achromium source and a pyrrolide ligand as being useful for thisprocess—see, for example, U.S. Pat. No. 5,198,563 (Reagen et al.,assigned to Phillips Petroleum).

Another family of highly active trimerization catalysts is disclosed byWass et al. in WO 02/04119 (now U.S. Pat. Nos. 7,141,633 and 6,800,702.The catalysts disclosed by Wass et al. are formed from a chromium sourceand a chelating diphosphine ligand and are described in further detailby Carter et al. (Chem. Comm. 2002, p 858-9). As described in the Chem.Comm. paper, these catalysts preferably comprise a diphosphine ligand inwhich both phosphine atoms are bonded to two phenyl groups that are eachsubstituted with an ortho-methoxy group. Hexene-1 is produced with highactivity and high selectivity by these catalysts.

Similar diphosphine/tetraphenyl ligands are disclosed by Blann et al. inWO04/056478 and WO 04/056479 (now US 2006/0229480 and US 2006/0173226).However, in comparison to the ligands of Wass et al., thedisphosphine/tetraphenyl ligands disclosed by Blann et al. generally donot contain polar substituents in ortho positions. The “tetraphenyl”diphosphine ligands claimed in the '480 application must not have orthosubstituents (of any kind) on all four of the phenyl groups and the“tetraphenyl” diphosphine ligands claimed in '226 are characterized byhaving a polar substituent in a meta or para position. Both of theseapproaches are shown to reduce the amount of hexenes produced andincrease the amount of octene (in comparison to the ligands of Wass etal.). However, the hexene fraction generally contains a large portion ofinternal hexenes, which is undesirable. Thus, chromium based catalystswhich contain the ligands of Blann et al. typically produce more octene(which may be advantageous if demand for octene is high) but theseligands have the disadvantage of producing a hexene stream which iscontaminated with a comparatively large amount of internal olefins.

Internal olefins are undesirable contaminants in linear low densitypolyethylene (LLDPE) production facilities because the internal olefinsare not readily incorporated into LLDPE with most transition metalcatalysts. Thus, it is preferable to remove/separate internal olefinsfrom alpha olefins if the alpha olefin is to be used in an LLDPEprocess. As will be appreciated by those skilled in the art, it iscomparatively difficult to separate hexene-1 from internal hexenes bydistillation due to the close boiling points of these hexene isomers.

Accordingly, a process which selectively produces high levels ofoctene-1 with very low levels of internal olefins in the co-producthexenes represents a desirable addition to the art. In addition, thepresent invention enables a selective oligomerization reaction withrelatively low amounts of polymer by-product.

DISCLOSURE OF INVENTION

In one embodiment, the present invention provides a new family of P-N-Pligands defined by the formula:

wherein Ar₁ is selected from the group consisting of aromatichydrocarbyl and aromatic heterohydrocarbyl; Ar^(F) is an aromaticfluorocarbyl oxide; Ar₃ and Ar₄ are independently selected from thegroup consisting of aromatic hydrocarbyl; aromatic heterohydrocarbyl andaromatic fluorocarbyl oxide; and R₁ is selected from the groupconsisting of hydrocarbyl and heterohydrocarbyl.

These molecules are particularly suitable for use as a ligand in aprocess to oligomerize ethylene. Potential alternative uses includeligands for hydrogenation and/or hydroformylation reactions.

A preferred example of a ligand according to this invention is definedby the following formula:

In another embodiment, this invention provides a process for theoligomerization of ethylene, wherein the process comprising contactingethylene with a catalyst system comprising i) a source of chromium; ii)a ligand defined by the formula:

wherein Ar₁, Ar^(F), R₁, Ar₃, and Ar₄ are as defined above.

-   and iii) an activator.

BEST MODE FOR CARRYING OUT THE INVENTION

The terms “substituted”, “hydrocarbyl”, “aromatic” and“heterohydrocarbyl” as used herein are intended to convey theirconventional meaning. Brief descriptions follow.

The term “substituted” (as in “substituted phenyl”) means that at leastone hydrogen atom bound to a carbon atom of the phenyl group is replacedwith a substituent or substituent group. For example, a phenyl group inwhich a hydrogen is replaced with a fluorine atom (especially in anortho position) provides a “fluoro substituted” group that are preferredligands of this invention.

The term “hydrocarbyl” refers to groups containing only carbon andhydrogen. Non-limiting examples of hydrocarbyl groups are thosecontaining from 1 to 50 carbon atoms, especially from 1 to 24 carbonatoms, most especially from 1 to 16 carbon atoms.

The term “heterohydrocarbyl” refers to a group containing at least oneatom in addition to carbon or hydrogen. Preferred heteroatoms includenitrogen, oxygen, sulfur, phosphorus, boron, chlorine, fluorine, andsilicon. The term fluorocarbyl refers to a group containing onlyfluorine and carbon. The term fluorocarbyl oxide refers to a group thatcontains fluorine, carbon and oxygen. Non-limiting examples offluorocarbyl oxides contain from six to twenty carbon atoms, especiallysix to twelve carbon atoms and a single oxygen atom.

The term “aromatic” refers to a cyclic ring group that includesunsaturation that is delocalized across the ring atoms.

The ligands of this invention contain at least one aromatic fluorocarbyloxide group that is bonded to a P atom and at least one hydrocarbyl orheterohydrocarbyl group that is bonded to a P atom.

A particularly preferred fluorocarbyl oxide group is

Particularly preferred hydrocarbyl groups are phenyl and substitutedphenyl (especially ortho-fluoro substituted phenyl).

Part A: Catalyst System

The catalyst system used in the process of the present invention mustcontain three essential components, namely:

(i) a source of chromium:

(ii) a defined P-N-P ligand; and

(iii) an activator.

Embodiments of each of these components are discussed below.

Chromium Source (“Component (i)”)

Any source of chromium which allows the oligomerization process of thepresent invention to proceed may be used. Common examples includechromium chlorides; chromium acetylacetonate, chromium carbonyl, andchromium carboxylates. Preferred chromium sources include chromiumtrichloride; chromium (III) 2-ethylhexanoate; chromium (III)acetylacetonate and chromium carboxyl complexes such as chromiumhexacarboxyl.

Ligand Used in the Oligomerization Process (“Component (ii)”)

In general, the ligand used in the oligomerization process of thisinvention is defined by the formula:

wherein Ar₁ is selected from the group consisting of aromatichydrocarbyl and aromatic heterohydrocarbyl; Ar^(F) is an aromaticfluorocarbyl oxide; Ar₃ and Ar₄ are independently selected from thegroup consisting of aromatic hydrocarbyl; aromatic heterohydrocarbyl andaromatic fluorocarbyl oxide; and R₁ is selected from the groupconsisting of hydrocarbyl and heterohydrocarbyl. For clarity, it is tobe emphasized that each of Ar₁, Ar^(F), Ar₃, and Ar₄ is an aromaticgroup.

It is preferred that each aromatic group contains only one ringstructure.

The use of unsubstituted phenyl and ortho-substituted phenyl isespecially preferred. Other non-limiting substituents are selected fromthe group consisting of C_(1 to 8) alkyl groups, and C_(1 to 4) alkoxygroups.

The Ar^(F) group is preferably C₆F₅O— (For clarity, this preferredAr^(F) group would become pentafluorophenol if a hydrogen atom were tobe bonded to the oxygen).

A novel and highly preferred ligand contains phenyl, ortho-substitutedphenyl and C₆F₅O, as shown in the examples.

The nitrogen atom of the P—N—P ligands of this invention contains agroup (denoted R₁, in the above formula) to satisfy the valence ofnitrogen. Non-limiting embodiments of this group include: a C₃ to C₅₀heterocarbyl group, or; a C_(1 to 20) alkyl, with isopropyl beingespecially preferred.

Activator (“Component (iii)”)

The activator (component (iii)) may be any compound that generates anactive catalyst for ethylene oligomerization with components (i) and(ii). Mixtures of activators may also be used. Suitable compoundsinclude organoaluminum compounds, organoboron compounds and inorganicacids and salts, such as tetrafluoroboric acid etherate, silvertetrafluoroborate, sodium hexafluoroantimonate and the like. Suitableorganoaluminum compounds include compounds of the formula AlR₃, whereeach R is independently C₁-C₁₂ alkyl, oxygen or halide, and compoundssuch as LiAlH₄ and the like. Examples include trimethylaluminum (TMA),triethylaluminum (TEA), tri-isobutylaluminium (TIBA),tri-n-octylaluminium, methylaluminium dichloride, ethylaluminiumdichloride, dimethylaluminium chloride, diethylaluminium chloride,ethylaluminiumsesquichloride, methylaluminiumsesquichloride, andalumoxanes. Alumoxanes are well known in the art as typically oligomericcompounds which can be prepared by the controlled addition of water toan alkylaluminium compound, for example trimethylaluminium. Suchcompounds can be linear, cyclic, cages or mixtures thereof. Commerciallyavailable alumoxanes are generally believed to be mixtures of linear andcyclic compounds. The cyclic alumoxanes can be represented by theformula [R⁶AlO]_(s) and the linear alumoxanes by the formulaR⁷(R⁸AlO)_(s) wherein s is a number from about 2 to about 50, andwherein R⁶, R⁷, and R⁸ represent hydrocarbyl groups, preferably C₁ to C₆alkyl groups, for example methyl, ethyl or butyl groups. Alkylalumoxanesespecially methylalumoxane (MAO) are preferred. (MAO is also referred toas methalumoxane and methylaluminoxane in the literature).

It will be recognized by those skilled in the art that commerciallyavailable alkylalumoxanes may contain a proportion of trialkylaluminium.For instance, commercial MAO usually contains approximately 10 wt %trimethylaluminium (TMA), and commercial “modified MAO” (or “MMAO”)contains both TMA and TIBA. Quantities of alkylalumoxane are generallyquoted herein on a molar basis of aluminium (and include such “free”trialkylaluminium). The alkylalumoxane and/or alkylaluminium may beadded to the reaction media (i.e. ethylene and/or diluent and/orsolvent) prior to the addition of the catalyst or at the same time asthe catalyst is added. Such techniques are known in the art ofoligomerization and are disclosed in more detail in for example, U.S.Pat. Nos. 5,491,272; 5,750,817; 5,856,257; 5,910,619; and 5,919,996.

Examples of suitable organoboron compounds are boroxines, NaBH₄,trimethylboron, triethylboron,dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate,triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate,sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate,trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl) boron.

Activator compound (iii) may also be or contain a compound that acts asa reducing or oxidizing agent, such as sodium or zinc metal and thelike, or oxygen and the like.

In the preparation of the catalyst systems used in the presentinvention, the quantity of activating compound to be employed is easilydetermined by simple testing, for example, by the preparation of smalltest samples which can be used to oligimerize small quantities ofethylene and thus to determine the activity of the produced catalyst. Itis generally found that the quantity employed is sufficient to provideabout 0.5 moles to about 1500 moles of aluminium (or boron) per mole ofchromium. MAO is the presently preferred activator. Molar Al/Cr ratiosof from about 1/1 to about 1500/1 are preferred. The ligand of thisinvention responds well to high levels of MAO, as shown in the examples.

Part B: Process Conditions

The chromium (component (i)) and ligand (component (ii)) may be presentin any molar ratio which produces oligomer, preferably between about100:1 and about 1:100, and most preferably from about 10:1 to about1:10, particularly about 3:1 to about 1:3. Generally the amounts of (i)and (ii) are approximately equal, i.e. a ratio of between about 1.5:1and about 1:1.5.

Components (i)-(iii) of the catalyst system utilized in the presentinvention may be added together simultaneously or sequentially, in anyorder, and in the presence or absence of ethylene in any suitablesolvent, so as to give an active catalyst. For example, components (i),(ii) and (iii) and ethylene may be contacted together simultaneously, orcomponents (i), (ii) and (iii) may be added together simultaneously orsequentially in any order and then contacted with ethylene, orcomponents (i) and (ii) may be added together to form an isolablemetal-ligand complex and then added to component (iii) and contactedwith ethylene, or components (i), (ii) and (iii) may be added togetherto form an isolable metal-ligand complex and then contacted withethylene. Suitable solvents for contacting the components of thecatalyst or catalyst system include, but are not limited to, hydrocarbonsolvents such as heptane, cyclohexane, toluene, 1-hexene and the like,and polar solvents such as diethyl ether, tetrahydrofuran, acetonitrile,dichloromethane, chloroform, chlorobenzene, methanol, acetone and thelike. The process may also be conducted as a “bulk process” (i.e. aprocess that is conducted in the presence of the reactants—withessentially no additional solvent or diluent being added).

The catalyst components (i), (ii) and (iii) utilized in the presentinvention can be unsupported or supported on a support material, forexample, silica, alumina, MgCl₂ or zirconia, or on a polymer, forexample polyethylene, polypropylene, polystyrene, or poly(aminostyrene).If desired the catalysts can be formed in situ in the presence of thesupport material, or the support material can be pre-impregnated orpremixed, simultaneously or sequentially, with one or more of thecatalyst components. The quantity of support material employed can varywidely, for example from about 100,000 grams to about 1 grams per gramof metal present in the transition metal compound. In some cases, thesupport material can also act as or as a component of the activatorcompound (iii). Examples include supports containing alumoxane moieties.

The oligomerization can be, conducted under solution phase, slurryphase, gas phase or bulk phase conditions. Suitable temperatures rangefrom about 10° C. to about 300° C. preferably from about 10° C. to about100° C., especially from about 30° C. to about 60° C. Suitable pressuresare from about atmospheric to about 800 atmospheres (gauge) preferablyfrom about 5 atmospheres to about 150 atmospheres, especially from about10 to about 50 atmospheres.

Irrespective of the process conditions employed, the oligomerization istypically carried out under conditions that substantially excludeoxygen, water, and other materials that act as catalyst poisons. Also,oligomerization can be carried out in the presence of additives tocontrol selectivity, enhance activity and reduce the amount of polymerformed in oligomerization processes. Potentially suitable additivesinclude, but are not limited to, hydrogen or a halide source. The use ofhydrogen is especially preferred as hydrogen has been observed tomitigate the formation of by-product polymer.

There exist a number of options for the oligomerization reactorincluding batch, semi-batch, and continuous operation. The reactions ofthe present invention can be performed under a range of processconditions that are readily apparent to those skilled in the art: as ahomogeneous liquid phase reaction in the presence or absence of an inerthydrocarbon diluent such as toluene or heptanes; as a two-phaseliquid/liquid reaction; as a slurry process where the catalyst is in aform that displays little or no solubility; as a bulk process in whichessentially neat reactant and/or product olefins serve as the dominantmedium; as a gas-phase process in which at least a portion of thereactant or product olefin(s) are transported to or from a supportedform of the catalyst via the gaseous state. Evaporative cooling from oneor more monomers or inert volatile liquids is but one method that can beemployed to effect the removal of heat from the reaction. The reactionsmay be performed in the known types of gas-phase reactors, such ascirculating bed, vertically or horizontally stirred-bed, fixed-bed, orfluidized-bed reactors, liquid-phase reactors, such as plug-flow,continuously stirred tank, or loop reactors, or combinations thereof. Awide range of methods for effecting product, reactant, and catalystseparation and/or purification are known to those skilled in the art andmay be employed: distillation, filtration, liquid-liquid separation,slurry settling, extraction, etc. One or more of these methods may beperformed separately from the oligomerization reaction or it may beadvantageous to integrate at least some with the reaction; anon-limiting example of this would be a process employing catalytic (orreactive) distillation. Also advantageous may be a process whichincludes more than one reactor, a catalyst kill system between reactorsor after the final reactor, or an integrated reactor/separator/purifier.While all catalyst components, reactants, inerts and products could beemployed in the present invention on a once-through basis, it is ofteneconomically advantageous to recycle one or more of these materials; inthe case of the catalyst system, this might require reconstituting oneor more of the catalysts components to achieve the active catalystsystem. It is within the scope of this invention that an oligomerizationproduct might also serve as a solvent or diluent. Mixtures of inertdiluents or solvents also could be employed. The preferred diluents orsolvents are aliphatic and aromatic hydrocarbons and halogenatedhydrocarbons such as, for example, isobutane, pentane, toluene, xylene,ethylbenzene, cumene, mesitylene, heptane, cyclohexane,methylcyclohexane, 1-hexene, 1-octene, chlorobenzene, dichlorobenzene,and the like, and mixtures such as Isopar™.

Techniques for varying the distribution of products from theoligomerization reactions include controlling process conditions (e.g.concentration of components (i)-(iii), reaction temperature, pressure,residence time) and properly selecting the design of the process and arewell known to those skilled in the art.

The ethylene feedstock for the oligomerization may be substantially pureor may contain other olefinic impurities and/or ethane. One embodimentof the process of the invention comprises the oligomerization ofethylene-containing waste streams from other chemical processes or acrude ethylene/ethane mixture from a cracker.

It is also within the scope of the present invention to conduct anoligomerization reaction in the presence of two or more oligomerizationcatalysts. In one embodiment, all of the oligomerization catalysts maybe prepared with variants of the present novel P-N-P ligands. In anotherembodiment, a different form of oligomerization catalyst may be used incombination with a catalyst prepared from the present P-N-P ligands.

In one embodiment of the present invention, the oligomerization productproduced from this invention is added to a product stream from anotheralpha olefins manufacturing process for separation into different alphaolefins. As previously discussed, “conventional alpha olefin plants”(wherein this term includes: i) those processes which produce alphaolefins by a chain growth process using an aluminum alkyl catalyst; ii)the aforementioned “SHOP” process, and; iii) the production of olefinsfrom synthesis gas using the so called Lurgi process) have a series ofdistillation columns to separate the “crude alpha product” (i.e. amixture of alpha olefins) into alpha olefins (such as butene-1, hexene-1and octene-1). The mixed hexene-octene product which is produced inaccordance with the present invention is highly suitable foraddition/mixing with a crude alpha olefin product from an existing alphaolefin plant (or a “cut” or fraction of the product from such a plant)because the mixed hexene-octene product produced in accordance with thepresent invention can have very low levels of internal olefins. Thus,the hexene-octene product of the present disclosure invention can bereadily separated in the existing distillation columns of alpha olefinplants (without causing the large burden on the operation of thesedistillation columns which would otherwise exist if the presenthexene-octene product stream contained large quantities of internalolefins). As used herein, the term “liquid product” is meant to refer tothe oligomers produced by the process of the present invention whichhave from 4 to (about) 20 carbon atoms.

The liquid product from the oligomerization process of the presentinvention preferably consists of from about 25 to about 70 weight %,especially from about 50 to about 70 weight % octene-1, where the weight% is expressed on the basis of the total weight of liquid product.

An embodiment of the oligomerization process of this invention is alsocharacterized by producing very low levels of internal olefins (i.e. lowlevels of hexene-2, hexene-3, octene-2, octene-3, etc.), with preferredlevels of less than about 10 weight % (especially less than about 5weight %) of the hexenes and octenes being internal olefins. Low levelsof internal olefins (e.g. hexene-2 or octene-2) are highly desirablebecause:

-   -   a) internal olefins generally have boiling points that are very        close to the boiling point of the corresponding alpha olefin        (and hence are difficult to separate olefins by distillation);        and        internal olefins are difficult to copolymerize with ethylene        using conventional catalysts (in comparison to alpha olefins)        and hence are not desired for use in most copolymerizations.

While not wishing to be bound by theory, it is believed that theortho-fluoro substituents of the preferred ligands are associated withthe low levels of internal olefins. In particular it is reported in theliterature that otherwise similar oligomerization ligands (i.e. P—N—Pligands which do not contain ortho-fluoro substituents) that producemixed octene/hexene products that are rich in octene generally producehigh levels of internal hexenes.

It is generally preferred to deactivate the oligomerization catalyst atthe end of the polymerization reaction. In general, many polar compounds(such as water, alcohols and carboxcylic acids) will deactivate thecatalyst. The use of alcohols and/or carboxcylic acids is preferred—andcombinations of both are contemplated.

It is also preferred to remove the catalyst (and by-product polymer, ifany) from the liquid product stream. Techniques for catalystdeactivation/product recovery that are known for use with otheroligomerization catalysts should also be generally suitable for use withthe present catalysts (see for example, U.S. Pat. Nos. 5,689,028 and5,340,785.

One embodiment of the present invention encompasses the use ofcomponents (i) (ii) and (iii) in conjunction with one or more types ofolefin polymerization catalyst system (iv) to oligomerize ethylene andsubsequently incorporate a portion of the oligomerization product(s)into a higher polymer.

Component (iv) may be one or more suitable polymerization catalystsystem(s), examples of which include, but are not limited to,conventional Ziegler-Natta catalysts, metallocene catalysts,monocyclopentadienyl or “constrained geometry” catalysts, phosphiniminecatalysts, heat activated supported chromium oxide catalysts (e.g.“Phillips”-type catalysts), late transition metal polymerizationcatalysts (e.g. diimine, diphosphine and salicylaldiminenickel/palladium catalysts, iron and cobalt pyridyldiimine catalysts andthe like) and other so-called “single site catalysts” (SSC's).

Ziegler-Natta catalysts, in general, consist of two main components. Onecomponent is an alkyl or hydride of a Group I to III metal, mostcommonly Al(Et)₃ or Al(iBu)₃ or Al(Et)₂Cl but also encompassing Grignardreagents, n-butyllithium, or dialkylzinc compounds. The second componentis a salt of a Group IV to VIII transition metal, most commonly halidesof titanium or vanadium such as TiCl₄, TiCl₃, VCl₄, or VOCl₃. Thecatalyst components when mixed, usually in a hydrocarbon solvent, mayform a homogeneous or heterogeneous product. Such catalysts may beimpregnated on a support, if desired, by means known to those skilled inthe art and so used in any of the major processes known forco-ordination catalysis of polyolefins such as solution, slurry, andgas-phase. In addition to the two major components described above,amounts of other compounds (typically electron donors) maybe added tofurther modify the polymerization behaviour or activity of the catalyst.

Metallocene catalysts, in general, consist of transition metalcomplexes, most commonly based on Group IV metals, ligated withcyclopentadienyl(Cp)-type groups. A wide range of structures of thistype of catalysts is known, including those with substituted, linkedand/or heteroatom-containing Cp groups, Cp groups fused to other ringsystems and the like. Additional activators, such as boranes oralumoxane, are often used and the catalysts may be supported, ifdesired.

Monocyclopentadienyl or “constrained geometry” catalysts, in general,consist of a transition metal complexes, most commonly based on Group IVmetals, ligated with one cyclopentadienyl(Cp)-type group, often linkedto additional donor group. A wide range of structures of this type ofcatalyst is known, including those with substituted, linked and/orheteroatom-containing Cp groups, Cp groups fused to other ring systemsand a range of linked and non-linked additional donor groups such asamides, amines and alkoxides. Additional activators, such as boranes oralumoxane, are often used and the catalysts may be supported, ifdesired.

A typical heat activated chromium oxide (Phillips) type catalyst employsa combination of a support material to which has first been added achromium-containing material wherein at least part of the chromium is inthe hexavalent state by heating in the presence of molecular oxygen. Thesupport is generally composed of about 80 to 100 wt. % silica, theremainder, if any, being selected from the group consisting ofrefractory metal oxides, such as aluminium, boria, magnesia, thoria,zirconia, titania and mixtures of two or more of these refractory metaloxides. Supports can also comprise alumina, aluminium phosphate, boronphosphate and mixtures thereof with each other or with silica. Thechromium compound is typically added to the support as a chromium (III)compound such as the acetate or acetylacetonate in order to avoid thetoxicity of chromium (VI). The raw catalyst is then calcined in air at atemperature between 250 and 1000° C. for a period of from a few secondsto several hours. This converts at least part of the chromium to thehexavalent state. Reduction of the Cr (VI) to its active form normallyoccurs in the polymerization reaction, but can be done at the end of thecalcination cycle with CO at about 350° C. Additional compounds, such asfluorine, aluminium and/or titanium may be added to the raw Phillipscatalyst to modify it.

Late transition metal and single site catalysts cover a wide range ofcatalyst structures based on metals across the transition series.

Component (iv) may also comprise one or more polymerization catalysts orcatalyst systems together with one or more additional oligomerizationcatalysts or catalyst systems. Suitable oligomerization catalystsinclude, but are not limited to, those that dimerise (for example,nickel phosphine dimerisation catalysts) or trimerise olefins orotherwise oligomerize olefins to, for example, a broader distribution of1-olefins (for example, iron and cobalt pyridyldiimine oligomerizationcatalysts).

Component (iv) may independently be supported or unsupported. Wherecomponents (i) and (ii) and optionally (iii) are supported, (iv) may beco-supported sequentially in any order or simultaneously on the samesupport or may be on a separate support. For some combinations, thecomponents (i) (iii) may be part or all of component (iv). For example,if component (iv) is a heat activated chromium oxide catalyst then thismay be (i), a chromium source and if component (iv) contains analumoxane activator then this may also be the optional activator (iii).

The components (i), (ii), (iii) and (iv) may be in essentially any molarratio that produces a polymer product. The precise ratio requireddepends on the relative reactivity of the components and also on thedesired properties of the product or catalyst systems.

An “in series” process could be conducted by first conducting theoligomerization reaction, then passing the oligomerization product to apolymerization reaction. In the case of an “in series” process variouspurification, analysis and control steps for the oligomeric productcould potentially be incorporated between the trimerization andsubsequent reaction stages. Recycling between reactors configured inseries is also possible. An example of such a process would be theoligomerization of ethylene in a single reactor with a catalystcomprising components (i)-(iii) followed by co-polymerization of theoligomerization product with ethylene in a separate, linked reactor togive branched polyethylene. Another example would be the oligomerizationof an ethylene-containing waste stream from a polyethylene process,followed by introduction of the oligomerization product back into thepolyethylene process as a co-monomer for the production of branchedpolyethylene.

An example of an “in situ” process is the production of branchedpolyethylene catalyzed by components (i)-(iv), added in any order suchthat the active catalytic species derived from components (i)-(iii) areat some point present in a reactor with component (iv).

Both the “in series” and “in situ” approaches can be adaptions ofcurrent polymerization technology for the process stages includingcomponent (iv). All major olefin existing polymerization processes,including multiple reactor processes, are considered adaptable to thisapproach. One adaption is the incorporation of an oligomerizationcatalyst bed into a recycle loop of a gas phase polymerization process,this could be as a side or recycle stream within the main fluidizationrecycle loop and or within the degassing recovery and recycle system.

Polymerization conditions when component (iv) is present can be, forexample, solution phase, slurry phase, gas phase or bulk phase, withtemperatures ranging from about −100° C. to about 300° C., and atpressures of atmospheric and above, particularly from about 1.5 to about50 atmospheres. Reaction conditions, will typically have a significantimpact upon the properties (e.g. density, melt index, yield) of thepolymer being made and it is likely that the polymer requirements willdictate many of the reaction variables. Reaction temperature,particularly in processes where it is important to operate below thesintering temperature of the polymer, will typically, and preferably, beprimarily selected to optimize the polymerization reaction conditions.Also, polymerization or copolymerization can be carried out in thepresence of additives to control polymer or copolymer molecular weights.The use of hydrogen gas as a means of controlling the average molecularweight of the polymer or copolymer applies generally to thepolymerization process of the present invention.

Slurry phase polymerization conditions or gas phase polymerizationconditions are particularly useful for the production of high or lowdensity grades of polyethylene, and polypropylene. In these processesthe polymerization conditions can be batch, continuous orsemi-continuous. Furthermore, one or more reactors may be used, e.g.from two to five reactors in series. Different reaction conditions, suchas different temperatures or hydrogen concentrations may be employed inthe different reactors.

Once the polymer product is discharged from the reactor, any associatedand absorbed hydrocarbons are substantially removed, or degassed, fromthe polymer by, for example, pressure let-down or gas purging usingfresh or recycled steam, nitrogen or light hydrocarbons (such asethylene). Recovered gaseous or liquid hydrocarbons may be recycled to apurification system or the polymerization zone.

In the slurry phase polymerization process the polymerization diluent iscompatible with the polymer(s) and catalysts, and may be an alkane suchas hexane, heptane, isobutane, or a mixture of hydrocarbons orparaffins. The polymerization zone can be, for example, an autoclave orsimilar reaction vessel, or a continuous liquid full loop reactor, e.g.of the type well-known in the manufacture of polyethylene by thePhillips Process. When the polymerization process of the presentinvention is carried out under slurry conditions the polymerization ispreferably carried out at a temperature above about 0° C., mostpreferably above about 15° C. Under slurry conditions the polymerizationtemperature is preferably maintained below the temperature at which thepolymer commences to soften or sinter in the presence of thepolymerization diluent. If the temperature is allowed to go above thelatter temperature, fouling of the reactor can occur. Adjustment of thepolymerization within these defined temperature ranges can provide auseful means of controlling the average molecular weight of the producedpolymer. A further useful means of controlling the molecular weight isto conduct the polymerization in the presence of hydrogen gas which actsas chain transfer agent. Generally, the higher the concentration ofhydrogen employed, the lower the average molecular weight of theproduced polymer.

In bulk polymerization processes, liquid monomer such as propylene isused as the polymerization medium.

Methods for operating gas phase polymerization processes are well knownin the art. Such methods generally involve agitating (e.g. by stirring,vibrating or fluidizing) a bed of catalyst, or a bed of the targetpolymer (i.e. polymer having the same or similar physical properties tothat which it is desired to make in the polymerization process)containing a catalyst, and feeding thereto a stream of monomer (underconditions such that at least part of the monomer polymerizes in contactwith the catalyst in the bed. The bed is generally cooled by theaddition of cool gas (e.g. recycled gaseous monomer) and/or volatileliquid (e.g. a volatile inert hydrocarbon, or gaseous monomer which hasbeen condensed to form a liquid). The polymer produced in, and isolatedfrom, gas phase processes forms directly a solid in the polymerizationzone and is free from, or substantially free from liquid. As is wellknown to those skilled in the art, if any liquid is allowed to enter thepolymerization zone of a gas phase polymerization process the quantityof liquid in the polymerization zone is small in relation to thequantity of polymer present. This is in contrast to “solution phase”processes wherein the polymer is formed dissolved in a solvent, and“slurry phase” processes wherein the polymer forms as a suspension in aliquid diluent.

The gas phase process can be operated under batch, semi-batch, orso-called “continuous” conditions. It is preferred to operate underconditions such that monomer is continuously recycled to an agitatedpolymerization zone containing polymerization catalyst, make-up monomerbeing provided to replace polymerized monomer, and continuously orintermittently withdrawing produced polymer from the polymerization zoneat a rate comparable to the rate of formation of the polymer, freshcatalyst being added to the polymerization zone to replace the catalystwithdrawn from the polymerization zone with the produced polymer.

Methods for operating gas phase fluidized bed processes for makingpolyethylene, ethylene copolymers and polypropylene are well known inthe art. The process can be operated, for example, in a verticalcylindrical reactor equipped with a perforated distribution plate tosupport the bed and to distribute the incoming fluidizing gas streamthrough the bed. The fluidizing gas circulating through the bed servesto remove the heat of polymerization from the bed and to supply monomerfor polymerization in the bed. Thus the fluidizing gas generallycomprises the monomer(s) normally together with some inert gas (e.g.nitrogen or inert hydrocarbons such as methane, ethane, propane, butane,pentane or hexane) and optionally with hydrogen as molecular weightmodifier. The hot fluidizing gas emerging from the top of the bed is ledoptionally through a velocity reduction zone (this can be a cylindricalportion of the reactor having a wider diameter) and, if desired, acyclone and or filters to disentrain fine solid particles from the gasstream. The hot gas is then led to a heat exchanger to remove at leastpart of the heat of polymerization. Catalysts are preferably fedcontinuously or at regular intervals to the bed. At start up of theprocess, the bed comprises fluidizable polymer which is preferablysimilar to the target polymer. Polymer is produced continuously withinthe bed by the polymerization of the monomer(s). Preferably means areprovided to discharge polymer from the bed continuously or at regularintervals to maintain the fluidized bed at the desired height. Theprocess is generally operated at relatively low pressure, for example,at 10 to 50 atmospheres, and at temperatures for example, between 50 and135° C. The temperature of the bed is maintained below the sinteringtemperature of the fluidized polymer to avoid problems of agglomeration.

In the gas phase fluidized bed process for polymerization of olefins theheat evolved by the exothermic polymerization reaction is normallyremoved from the polymerization zone (i.e. the fluidized bed) by meansof the fluidizing gas stream as described above. The hot reactor gasemerging from the top of the bed is led through one or more heatexchangers wherein the gas is cooled. The cooled reactor gas, togetherwith any make-up gas, is then recycled to the base of the bed. In thegas phase fluidized bed polymerization process of the present inventionit is desirable to provide additional cooling of the bed (and therebyimprove the space time yield of the process) by feeding a volatileliquid to the bed under conditions such that the liquid evaporates inthe bed thereby absorbing additional heat of polymerization from the bedby the “latent heat of evaporation” effect. When the hot recycle gasfrom the bed enters the heat exchanger, the volatile liquid can condenseout. In one embodiment of the present invention the volatile liquid isseparated from the recycle gas and reintroduced separately into the bed.Thus, for example, the volatile liquid can be separated and sprayed intothe bed. In another embodiment of the present invention the volatileliquid is recycled to the bed with the recycle gas. Thus the volatileliquid can be condensed from the fluidizing gas stream emerging from thereactor and can be recycled to the bed with recycle gas, or can beseparated from the recycle gas and then returned to the bed.

A number of process options can be envisaged when using the catalysts ofthe present invention in an integrated process to prepare higherpolymers i.e. when component (iv) is present. These options include “inseries” processes in which the oligomerization and subsequentpolymerization are carried in separate but linked reactors and “in situ”processes in which a both reaction steps are carried out in the samereactor.

In the case of a gas phase “in situ” polymerization process, component(iv) can, for example, be introduced into the polymerization reactionzone in liquid form, for example, as a solution in a substantially inertliquid diluent. Components (i)-(iv) may be independently added to anypart of the polymerization reactor simultaneously or sequentiallytogether or separately. Under these circumstances it is preferred theliquid containing the component(s) is sprayed as fine droplets into thepolymerization zone. The droplet diameter is preferably within the rangefrom about 1 microns to about 1000 microns.

Although not usually required, upon completion of polymerization orcopolymerization, or when it is desired to terminate polymerization orcopolymerization or at least temporarily deactivate the catalyst orcatalyst component of this invention, the catalyst can be contacted withwater, alcohols, acetone, or other suitable catalyst deactivators amanner known to persons of skill in the art.

A range of polyethylene polymers are considered accessible includinghigh density polyethylene, medium density polyethylene, low densitypolyethylene, ultra low density polyethylene and elastomeric materials.Particularly important are the polymers having a density in the range of0.91 to 0.93, grams per cubic centimeter (g/cc) generally referred to inthe art as linear low density polyethylene. Such polymers and copolymersare used extensively in the manufacture of flexible blown or cast film.

Depending upon the use of the polymer product, minor amounts ofadditives are typically incorporated into the polymer formulation suchas acid scavengers, antioxidants, stabilizers, and the like. Generally,these additives are incorporated at levels of about 25 to 2,000 partsper million by weight (ppm), typically from about 50 ppm to about 1000ppm, and more typically from about 400 ppm to about 1,000 ppm, based onthe polymer. In use, polymers or copolymers made according to theinvention in the form of a powder are conventionally compounded intopellets. Examples of uses for polymer compositions made according to theinvention include use to form fibres, extruded films, tapes, spunbondedwebs, molded or thermoformed products, and the like. The polymers may beblown or cast into films, or may be used for making a variety of moldedor extruded articles such as pipes, and containers such as bottles ordrums. Specific additive packages for each application may be selectedas known in the art. Examples of supplemental additives include slipagents, anti-blocks, anti-stats, mould release agents, primary andsecondary anti-oxidants, clarifiers, nucleants, uv stabilizers, and thelike. Classes of additives are well known in the art and includephosphite antioxidants, hydroxylamine (such as N,N-dialkylhydroxylamine) and amine oxide (such as dialkyl methyl amine oxide)antioxidants, hindered amine light (uv) stabilizers, phenolicstabilizers, benzofuranone stabilizers, and the like.

Fillers such as silica, glass fibers, talc, and the like, nucleatingagents, and colourants also may be added to the polymer compositions asknown by the art.

The present invention is illustrated in more detail by the followingnon-limiting examples.

EXAMPLES

The following abbreviations are used in the examples:

-   A=Angstrom units-   NMR=nuclear magnetic resonance-   Et=ethyl-   Bu=butyl-   iPr=isopropyl-   H₂=hydrogen-   Psi=pounds per square inch-   rpm=revolutions per minute-   GC=gas chromatography-   FID=Flame Ionization Detector-   R_(X)=reaction-   Wt=weight-   C₆'s=hexenes-   C₈'s=octenes-   MAO=Methylalumoxane-   THF=tetrahydrofuran    Ligand Synthesis    General Experimental Conditions for Ligand Synthesis

All reactions involving air and/or moisture sensitive compounds wereconducted under nitrogen using standard Schlenk and glovebox techniques.Reaction solvents were purified prior to use (e.g. by distillation) andstored over activated 13× molecular sieves. Diethylamine, triethylamineand isopropylamine were purchased from Aldrich and dried over 13×molecular sieves prior to use. 1-Bromo-2-fluoro-benzene, phosphorustrichloride (PCl_(S)), hydrogen chloride gas and n-butyllithium werepurchased from Aldrich and used as is. The methalumoxane (MAO) waspurchased from Akzo and used as is. Deuterated solvents were purchased(CD₂Cl₂, toluene-d₈, THF-d₈) and were stored over 13× molecular sieves.NMR spectra were recorded on a Bruker 400 MHz spectrometer. ThePreparation of Et₂NPCl₂, (ortho-F—C₆H₄)₂P—NEt₂, (ortho-F—C₆H₄)₂PCl and(ortho-F—C₆H₄)₂PNH(i-Pr) is known in the literature (e.g. U.S. Pat. No.7,994,363).

Preparation of (ortho-F—C₆H₄)₂PN(i-Pr)PCl(Ph)

(ortho-F—C₆H₄)₂PNH(i-Pr) (2.001 g, 7.16 mmol) in 40 mL pentane wascooled to −70° C. n-butyllithium (4.48 mL, 1.6M in hexane, 7.16 mmol)was added dropwise yielding a beige slurry that was stirred at −78° C.for one hour and then warmed slowly to 10° C. The solution was thencooled back down to −10° C. and was added to dichlorophenylphosphine(1.279 g, 7.15 mmol) in 30 mL pentane at −70° C. dropwise over 30minutes yielding a beige slurry that was stirred for one hour at −70° C.then warmed to room temperature. Volatiles were removed via vacuum. Thebeige solid was reslurried in 40 mL pentane. Solid was filtered off andwashed twice with 10 mL pentane. The filtrate was pumped down to 20%volume and solution was recrystallized overnight yielding a white solidthat was filtered and washed with cold pentane and dried to 300 mTorr.The yield of this reaction was essential quantitative. ¹H NMR (δ,DCM-d₂): 7.85-7.18 (m, 13H), 3.86 (m, 1H), 1.32 (d, 4H), 1.04 (d, 3H).³¹P NMR (δ, DCM-d₂): 134.59 (s), 21.01 (s). ¹⁹F NMR (δ, DCM-d₂): −105.49(d), −106.44 (d). Single crystal X-Ray structural determinationconfirmed the structure of this compound.

Preparation of (ortho-F—C₆H₄)₂PN(i-Pr)P(Ph)(OC₆F₅)

Pentafluorophenol (0.191 g, 1.04 mmol) in 5 mL diethyl ether was addeddropwise to (ortho-F—C₆H₄)₂PN(i-Pr)PCl(Ph) (0.424 g, 1.01 mmol) andtriethylamine (0.17 mL, 1.22 mmol) in 15 mL of diethyl ether at −70° C.The cloudy white solution was warmed to room temperature overnightyielding a white slurry which was pumped down to 300 mTorr. The productwas extracted in pentane and was isolated from the precipitate byfiltration. The volume of the pentane solution was reduced to a coupleof milliliters and product recrystallized overnight. The white solid wasisolated by decanting mother liquor and was dried under vacuum to 300mTorr. ¹H NMR (δ, DCM-d₂): 7.62-6.90 (m, 13H), 3.94, (m, 1H), 1.45 (d,3H), 1.05 (d, 3H). ³¹P NMR (δ, DCM-d₂): 149.78 (s), 15.00 (s). ¹⁹F NMR(δ, DCM-d₂): −105.23 (d), −106.02 (d), −158.39 (dd), −166.87 (t),−168.31 (t). This product (referred to as Ligand 1) was used in theoligomerization examples of Part B that follows.Part BEthylene Oligomerization

A continuous stirred tank reactor having a volume of 1000 cc was usedfor these experiments. A range of operating conditions were tested.

Reactor temperatures between about 60° C. and 80° C. and at a pressuresof 8 MPa were tested.

The reactor was fitted with external jacket cooling. A feed preparationunit was installed to allow ethylene to be dissolved in solvent prior tobeing added to the reactor.

MAO was purchased as a solution of modified methylaluminoxane (7 weight% Al in isopentane) from Akzo Nobel.

The reactor was operated in a continuous manner—i.e. product was removedfrom the reactor during the reaction and make-up feed was added. Typicalflow rates and reactor concentrations were as follows:

-   -   Chromium (as Cr(acetylacetonate)₃): 0.00125-0.0025 mmol/liter    -   Ligand/Cr mole ratio=1.8/1    -   Al/Cr mole ratio=900/1 (Akzo MMAO-3A)    -   Ethylene feed rate=8 g/minute    -   MAO solution+cyclohexane ˜33 ml/minute        The liquid fraction produced in these experiments were typically        greater than 95% alpha olefins. The reactor was also equipped        with hydrogen feed capabilities.

TABLE 1 Reactor Reactor Hold-up Ethylene Activity Run Temp TimeConversion (gProduct/ C6, C8, C10+ # (° C.) (Hr.) (%) gCr · hr) wt % wt% wt % 1 60 0.5 78.8 2,871,255 49.3 31.3 16.2 2 70 0.5 81.3 2,962,34852.7 26.3 17.8 3 80 0.5 78.5 2,860,324 55.6 25.2 16.0 4 80 1.0 81.22,958,704 51.5 28.4 16.7

Ethylene flow=8 g/min.

Hydrogen flow=0.018 g/min.

Reactor pressure=8 MPa

[Cr]=0.00253 mmol/liter

Al/Cr (molar)=900/1

Ligand/Cr (molar)=1.8/1

Ligand 1 from Part A was used in all examples

The level of polymer production was less than 1% of the reactedethylene. 97% hexene-1 purity was observed in all of the hexenes.

INDUSTRIAL APPLICABILITY

A new phosphorous-nitrogen-phosphorous (“P-N-P”) ligand is provided. Thecombination of this ligand with a source of a catalytic chromium metaland an activator (such as methylaluminoxane) is useful for the selectiveoligomerization of ethylene. The resulting oligomers are predominantlylinear alpha olefins (especially octene and hexene) which are useful ascomonomers for the production of ethylene-alpha olefin copolymers.

What is claimed is:
 1. A ligand defined by the formula:

wherein Ar1 is selected from the group consisting of aromatic hydrocarbyl and aromatic heterohydrocarbyl; ArF is an aromatic fluorocarbyl oxide; Ar3 and Ar4 are independently selected from the group consisting of aromatic hydrocarbyl; aromatic heterohydrocarbyl and aromatic fluorocarbyl oxide; and R1 is selected from the group consisting of hydrocarbyl and heterohydrocarbyl.
 2. The ligand of claim 1 wherein ArF is


3. The ligand of claim 2 wherein each of Ar1, Ar3, and Ar4 is aromatic hydrocarbyl.
 4. The ligand of claim 3 wherein Ar1 is phenyl and Ar3 and Ar4 are ortho-fluoro substituted phenyl.
 5. The ligand of claim 1 wherein R1 is a C1 to 20 hydrocarbyl.
 6. The ligand of claim 5 wherein R1 is isopropyl.
 7. The molecule: 